This invention relates to a biaxial actuator for an optical pickup of an optical disc recording and reproduction device using an optical disc such as for example a CD, LD, MO or MD.
This kind of biaxial actuator for an optical pickup is used in recording and reproducing signals to and from an optical disc such as for example a CD, LD, MO or MD. This actuator moves an objective lens mounted on a supporting member in two directions, a focussing direction and a tracking direction.
Among biaxial actuators of this kind, there are for example those constituted as shown in FIG. 1. Referring to FIG. 1, a biaxial actuator 100 comprises a slide base 103 mounted on a reference shaft 102, an inclination angle adjusting plate 104 mounted for oscillatory movement on the slide base 103, an XY adjusting plate 105 mounted on this inclination angle adjusting plate 104, a lens holder 106 mounted on the XY adjusting plate 105, and an actuator cover 107 disposed covering the lens holder 106 from the sides and from above.
The slide base 103 is mounted movably along the reference shaft 102. When the slide base 103 moves along the reference shaft 102, an objective lens 106a mounted in the lens holder 106 moves in the radial direction of an optical disc.
In the example shown in FIG. 1, a downwardly projecting convex portion 104a of the inclination angle adjusting plate 104 fits in a concave recess 103a provided in the upper surface of the slide base 103, and this convex portion 104a slides in the concave recess 103a. As a result, the inclination angle adjusting plate 104 can oscillate in any direction with respect to the slide base 103.
The XY adjusting plate 105 is mounted movably in two horizontal directions, namely X and Y directions, with respect to this inclination angle adjusting plate 104, and inclination of the lens holder 106 is thereby corrected.
The lens holder 106 is mounted by way of a suspension 106b movably in two directions orthogonal to the direction toward the XY adjusting plate 105, namely a tracking direction and a focussing direction.
The actuator cover 107 is fixed to the XY adjusting plate 105 and covers the lens holder 106 from the sides and from above without obstructing movement of the lens holder 106 in the tracking direction and in the focussing direction.
In the biaxial actuator 100 so constituted, by drive voltages being supplied to drive coils mounted on the lens holder 106, magnetic flux generated at the drive coils interacts with magnetic flux from a yoke and magnets (not shown in FIG. 1) mounted on the XY adjusting plate 105. As a result, the objective lens 106a mounted in the lens holder 106 moves in the focussing direction and the tracking direction.
However, in this kind of biaxial actuator adjusting device, the stroke of the lens holder 106 in the focussing direction is limited in the following way:
The upward stroke extent P of the lens holder 106 is limited by the top of the lens holder 106 abutting with the inner surface of the actuator cover 107. The downward stroke extent Q of the lens holder 106 is limited by the bottom of the lens holder 106 abutting with the upper surface of the XY adjusting plate 105.
As shown in FIG. 1, the position of the inner surface of the actuator cover 107 is decided by the dimension A between the upper surface of the slide base 103 and the center of the reference shaft 102, the dimension B of the inclination angle adjusting plate 104, the dimension C of the XY adjusting plate 105 and the dimension D of the actuator cover 107.
Therefore, the position of the inner surface of the actuator cover 107, that is, the upward stroke extent P of the lens holder 106, has dimensional dispersion depending on the dimensional accuracy of the dimensions A, B, C and D of the above-mentioned members.
Also, the position of the upper surface of the XY adjusting plate, as shown in FIG. 1, is decided by the dimension A between the upper surface of the slide base 103 and the center of the reference shaft 102, the dimension B of the inclination angle adjusting plate 104 and the dimension C of the XY adjusting plate 105.
Therefore, the position of the upper surface of the XY adjusting plate 105, that is, the downward stroke extent Q of the lens holder 106, has dimensional dispersion depending on the dimensional accuracy of the dimensions A, B and C of the above members.
Thus there has been the problem that relatively large dispersions occur in the upward stroke extent P and the downward stroke extent Q of the lens holder 106 depending on the dimensional accuracy of the slide base 103, the inclination angle adjusting plate 104, the XY adjusting plate 105 and the actuator cover 107.
Also, when the lens holder 106 is mounted diagonally with respect to the XY adjusting plate 105, as shown in FIG. 2, although this inclination of the lens holder 106 is corrected by the inclination angle adjusting plate 104, there has been the problem that because the lens holder 106 is at an incline in the space bounded by the XY adjusting plate 105 and the actuator cover 107, compared to when the lens holder 106 is mounted substantially horizontally with respect to the XY adjusting plate 105 the upward stroke extent P and the downward stroke extent Q are more limited.
A biaxial actuator has a lens holder in the end of which an objective lens is mounted and a coil bobbin mounted on this lens holder using adhesive or the like.
The lens holder is mounted movably in two directions orthogonal to a fixed part, namely the tracking direction and the focussing direction, by way of two sheet springs each having one end fixed to one side of the lens holder and the other end fixed to the fixed part
The coil bobbin has a focussing coil and a tracking coil wound thereon. Magnetic flux generated at the coils by current being passed through the coils interacts with magnetic flux from a yoke mounted on the fixed part and magnets mounted on the yoke.
Here, the above-mentioned yoke is mounted as shown in FIG. 3. That is, referring to FIG. 3, in a biaxial actuator 200, an actuator cover 204 is mounted from above on a yoke 203 fixed to a biaxial base 202 of the biaxial actuator 200.
The yoke 203 has a yoke portion 203b extending upward from two sides of a flat base 203a so as to form a U-shape (not shown in FIG. 3). This yoke portion 203b, when seen from the side, as shown in FIG. 3, has projecting portions 203c and 203d extending to the front and rear so that the overall yoke portion 203b forms a T-shape, and projections 203e and 203f extending upward from the upper edge.
The actuator cover 204 has large openings on both sides and has hooks 204a and 204b extending downward from two places on both side edges thereof. These hooks 204a and 204b have engaging claws 204c projecting inward from their lower ends as shown in FIG. 5.
In a biaxial actuator 200 thus constituted, by the actuator cover 204 being placed on the yoke 203 the lower end 204d of the actuator cover 204 abuts with the upper surfaces of the projections 203e and 203f of the yoke portion 203b of the yoke 203 (see FIG. 4). The hooks 204a and 204b of the actuator cover 204 grip the yoke portion 203b of the yoke 203 from both sides.
The engaging claws 204c at the ends of the hooks 204a and 204b engage with the lower edges of the projecting portions 203c and 203d of the yoke portion 203b. As a result, the actuator cover 204 is held on the yoke 203 and covers above the biaxial base 202.
However, in a biaxial actuator 200 of this kind of constitution, because the width t1 of the lower ends 204d of both side edges of the actuator cover 204 is larger than the width t2 between the outer sides of the projections 203e and 203f on the yoke portion 203b of the yoke 203, there is a looseness between the yoke 203 and the actuator cover 204. When an effort is made to eliminate this looseness the width t1 is made slightly smaller than the width t2 resulting in a slight press-fit, there has been the problem that the actuator cover 204 is deformed.
Also, because as shown in FIG. 5 the thickness t3 and the width w of the hooks 204a and 204b are relatively small and the hooks are relatively long, they deform easily. As a result, they have sometimes disengaged from the lower edges of the projecting portions 203c and 203d of the yoke portion 203b of the yoke 203.
Also, because the width t2 between the outer sides of the projections 203e and 203f is relatively small compared to the overall length of the actuator cover 204, the stability of the actuator cover 204 is not very good. There has also been the problem that because the rear end portion of the actuator cover 204 abuts the biaxial base 202 it tends to slip.